The present embodiments relate to flameless thermal oxidizers (FTO) used to oxidize effluent or waste streams of for example chemical or petrochemical plants, and in particular to FTOs having a fixed matrix bed.
A flameless thermal oxidizer (FTO) is used for flameless oxidation of gaseous effluent (waste) streams, by introducing a mixture of the effluent stream and an oxidizer, typicallsy air, into an FTO vessel containing a fixed matrix bed maintained at temperatures above 1400° F. in a well defined reaction zone remote from a mixing region. During operation of a known FTO, a mixture of an effluent gaseous stream and an oxidizer is delivered to the fixed matrix bed through a dip tube partially embedded in the matrix such that an oxidation reaction zone, which is flameless, is established in the hot fixed matrix bed. An important difference between an FTO and other known types of combustors, such as burners, combustion chambers using coal or fluidized bed reactors, etc., is that within the FTO the oxidation reaction occurs outside of flammability limits, typicallsy below lower flammability limits (LFL) and thus, there is no flame front or the oxidation is flameless.
A combination of structural features and gaseous mixture controls in the known FTO prevents the oxidation reaction front from propagating upstream through the dip tube, thus making the FTO operationally safe as well as environment friendly. However, current FTO construction and related methods of operation do not offer the safety and environmental benefits in situations where the effluent mixture contains hydrogen gas. Hydrogen gas is extremely reactive, has a high oxidation reaction propagation velocity or flame speed, and when mixed with an oxidizer such as air, has a wide range of lower flammability to upper flammability limits, thus making known FTOs and related operations highly prone to a risk of uncontrolled oxidation reaction this uncontrolled oxidation reaction. This uncontrolled oxidation reaction will develop a flame front along an interior of the dip tube or inside the fixed matrix bed, thus creating conditions which may cause damage to the FTO vessel, violation of environmental permit limits on emission of volatile organic chemicals (VOCs), and/or green-house gases (GHGs).
The current lack of technical knowledge to control the oxidation mixture concentration limits, mixture speed, and reaction zone necessary for effluent streams with hydrogen therein has to date prevented known FTOs from being used as a viable technical solution for such hydrogen laden gaseous streams.